This invention relates to electrostatographic reproduction machines, and more particularly to a liquid electrostatographic reproduction machine having a pressure differential nip image processing apparatus.
A typical electrostatographic reproduction machine employs a photoconductive or dielectric member that is sensitized by charging to a substantially uniform potential. The charged portion of the photoconductive member is exposed to the light image of a document. Exposure of the charged photoconductive member selectively dissipates the charge to record an electrostatic latent image. The electrostatic latent image corresponds to the informational areas of the document. As is also known, such a latent image can be formed equally using an ionographic or other equivalent process. The electrostatic latent image recorded on the photoconductive member is developed by contact with a developer material. The developer material can be a dry material comprising carrier granules having adhering toner particles. The latent image attracts the toner particles from the carrier granules to form a toner powder image on the photoconductive surface. The toner powder image is then transferred and permanently fused to a copy sheet.
An electrostatic latent image also may be developed by a liquid development system with a liquid developer material. In a liquid development system, the photoconductive surface is contacted with an insulating liquid carrier having dispersed finely divided charged marking particles. The electrical field associated with the electrostatic latent image attracts the charged marking particles to the photoconductive surface to form a visible image.
Liquid developing imaging processes utilize a liquid developer typically having about 2 percent by weight of fine solid particulate toner material dispersed in a liquid carrier. The liquid carrier is typically a hydrocarbon. In the developing process, the image is transferred to a receiver which may be an intermediate belt. The image on the photoreceptor contains about 12 weight percent of particulate toner in hydrocarbon carrier liquid. To improve the quality of transfer of a developed liquid toner image to a receiver, percent solids in liquid should be increased to about 25 percent by weight. Such an increase in percent solids may be achieved by removing excess hydrocarbon carrier liquid. However, excess hydrocarbon carrier liquid must be removed in a manner that results in minimum degradation of the toner image, as well as in minimal air pollution from evaporation of liquid carrier.
Examples of various devices for removing excess hydrocarbon carrier liquid from liquid toner developed images are disclosed in the following references.
U.S. Pat. No. 4,023,899 issued May 17, 1977, to Hayoski et al. discloses a controlled-gap and controlled-velocity hard roller for effecting removal of such liquid.
U.S. Pat. No. 4,181,094 issued Jan. 1, 1980, to Gardiner discloses a mechanical barrier including an air pressure slot. The barrier is positioned spaced from the image surface, a gap closer than the thickness of liquid developer. Compressed air is introduced into the barrier and focused directly onto the image-surface through the slot.
U.S. Pat. No. 4,259,006 issued Mar. 31, 1981, to Phillips et al. discloses an air knife devices for focusing a jet of air at about an angle of 45 directly onto the image surface.
U.S. Pat. No. 5,063,413 issued Nov. 5, 1991, to Domoto et al. discloses apparatus for focusing air flow directly along the image surface in a direction parallel and opposite to the direction of movement of the image surface.
There are disadvantages associated with these types of excess carrier liquid removing devices. The roller type devices tend to damage the toner image on the image surface or photoreceptor particularly where the roller is brought into pressing engagement with the surface of the photoreceptor or image surface. Usually, difficulty is also experienced in obtaining a roller that has a sufficiently smooth and planar peripheral surface so as to maintain good adherence of toner images on the photoreceptor, as well as, in synchronizing the rotation of the roller with movement of the photoreceptor. In the air knife type, the moving air directly contacts and vaporizes carrier liquid. The air then tends to become polluted by such vaporization of the carrier liquid. Additionally, the image on the photoreceptor usually is undesirably splashed with the blown carrier liquid. Also, noise is caused by the moving air stream, and the toner on the photoreceptor is blown by the air causing distortion of the image. It is generally also difficult to apply a uniform moving air stream to the photoreceptor.